Drive pods are becoming more common in marine applications, such as pleasure boats and other recreational watercraft. The drive pods offer better efficiency and lower noise compared to a traditional shaft and propeller drive system. To protect the integrity of the hull, drive pods are designed to separate from a boat hull if an underwater obstruction is encountered. Care must be taken in designing the drive pod so that the hull remains watertight after an impact that causes the drive pod to detach.
For example, U.S. Pat. No. 8,011,983 (the '983 patent) describes a breakaway mount in which an upper drive shaft and a lower drive shafts are connected via a coupler that allows the lower drive shaft and/or coupler to drop off when the drive pod detaches. However, shear forces applied to the drive pod may cause either the upper or lower drive shafts to fail at a point away from the coupler resulting in one or more of several undesirable outcomes. One undesirable outcome is damage to seals necessary for hull integrity and may pose a threat of sinking the boat. Another undesirable outcome is damage to seals in the drive pod that may allow the drive pod to leak oil into the environment, take on seawater which may further damage the drive pod, or both. The '983 patent fails to disclose a lower drive shaft assembly that consistently channels impact forces to a single point of failure.